1. Field of the Invention
The present invention relates to a cooling system for a computer, and more specifically, to a fan speed controlling cooling system for a personal computer.
2. Description of the Prior Art
As computer processing speeds steadily increase, the need for high capacity cooling systems becomes essential. Proper cooling prevents heat related failure of the processor when under operating loads. Typical cooling systems have progressed beyond the venerable constantly running fan to include temperature sensors and related control circuits for dynamically adjusting fan speed. While several fan speed control schemes have been developed, nearly all focus entirely on maximizing cooling effects or reducing power consumption. One aspect of fan control has been continuously neglected in development of control schemes and related circuitry, that is, fan noise level.
In the article Hanrahan, D. “Fan-Speed Control Techniques in PCs” Analog Dialogue Vol.34, No.4 (June-July 2000), which is incorporated herein by reference, several fan speed control schemes and circuits are described in detail. The first is a two-step fan control method in which a thermistor installed near a CPU or an on-die thermal monitoring transistor outputs a system temperature to a BIOS. The BIOS then switches a cooling fan on or off depending on the system temperature, a marked improvement over a constantly running fan. Similar to the two-step method, a three-step fan control method adds an additional half-speed setting for the fan. The half-speed setting is enabled when the processor is engaged in light duty generating little heat. The third method, a linear fan-speed control method, includes digital logic components that enable a range fan speeds based on the measured system temperature. The linear method is quite simply an extension of the three-speed method. Finally, a similar pulsewidth-modulation fan-speed control method allows fan speed to be controlled by adjusting fan signal duty cycle. While these are just a sampling of conventional fan speed control methods, they are representative of the current technology.
To realize linear fan-speed control methods such as that described above, circuits having the required operational logic have been developed. FIG. 1 illustrates a general state-of-the-art computer fan speed control circuit 10. The circuit 10 includes a fan 12 connected to a chipset controller 14 through a fan input-output interface 16. Generally, the chipset controller 14 contains logic linearly relating fan speeds to measured temperatures, and generates and outputs a corresponding control signal. Based on a temperature measured at a sensor 18, the chipset controller 14 outputs the control signal to the fan I/O 16, which controls the rotational speed of the fan 12. In an example of a specific conventional implementation, subcomponents of the blocks of the circuit 10 are as disclosed in Steele, J. “An I2C Fan for Personal Computers” Electronic Design Aug. 3, 1998, which is incorporated herein by reference. In an example of a linear fan-speed control method, the chipset controller 14 is programmed with a series of trigger temperatures and a corresponding series of signals having encoded fan speeds, which are directly proportional to the series of trigger temperatures. Thus, the controller 14 outputs a fan control signal identifying a fan speed corresponding to the temperature trigger reached.
The prior art methods of controlling a fan to cool a processor cannot suitably meet current cooling requirements. Having been developed for performance and power savings, these methods typically suffer in other areas of concern. Specifically, noise levels can be uncomfortably high in conventional fan cooling applications.